This invention relates to blood pumps, particularly to a temporary circulatory assist pump adapted for insertion into the vascular system of a patient to provide temporary circulatory assistance for a dyskinetic left or right ventricle of the heart.
Death and disability from heart disease are most commonly due to the pumping inadequacy of an infarcted left or right ventricle. The heart of a patient suffering from this condition functions in many other respects but does not provide sufficient blood flow to keep the patient alive. Typically, a patient suffering from this condition would require major surgery to maintain the heart and provide sufficient blood flow for the patient.
Another area where temporary circulatory assistance may be required is in allograft cardiac replacement or heart transplants. Although one year survivals after a heart transplant now approach 80%, a great many patients die waiting for a transplant, as do many of the 20% who might be saved by circulatory assistance while immunosuppressive agents are combating the body's natural rejection response of a transplanted heart. There is a great need for an effective circulatory assist pump for maintaining the life of a patient until the transplant can be accomplished and the allograft is stabilized. As the average life expectancy of the U.S. population continues to increase, coronary artery disease and chronic congestive heart failure can be expected to significantly increase the utilization of mechanical circulatory assistance. A realistic estimate of the number of potential candidates for mechanical circulatory assistance would be approximately 300,000 patients each year in the United States. This number will grow at a rate of 6% per year until the population of "baby boomers" peaks around the year 2020.
Methods and apparatus exist in the prior art for circulatory assistance of a heart. In U.S. Pat. No. 4,625,712 a high capacity intravascular blood pump is disclosed. The pump in inserted into the heart through the femoral artery and driven via a flexible cable from an external power source. The drive cable is contained within a catheter attached to the pump. The pump is rotated in the range of 10,000-20,000 rpm to produce blood flow on the order of 4 liters per minute.
U.S. Pat. No. 3,505,987 discloses a counterpulsation system for aiding coronary circulation. The system includes an expandable impeller located within the aorta of a patient. The impeller is expanded and contracted while simultaneously being reciprocated within the aorta and synchronized with the pumping activity of the heart for reducing aortic pressure during systole and increasing aortic pressure during diastole.
U.S. Pat. No. 3,667,069 discloses an implantable jet pump for replacing or assisting the right heart. The jet pump comprises an elongated tubular structure including an upstream driving nozzle from which a driving flow of arterial blood under pressure is ejected into a suction nozzle creating its own reduced pressure to cause venous blood to be sucked into and admixed with the driving flow for distribution to the pulmonary circulation system. The jet pump may be powered by blood pumped from the left heart or an artificial replacement for the left heart.
U.S. Pat. No. 4,051,840 discloses an aortic patch which may be surgically implanted in the thoracic aorta. The aortic patch is systematically inflated and deflated to generate pressure waves in the blood stream. The pressure waves assist the heart by augmenting the circulation of the blood to the body.
Generally, the methods available for circulatory assistance of the heart require major surgery for the implantation of the device which presents a great risk to the survival of the patient. The device disclosed in U.S. Pat. No. 4,625,712 may be introduced into the heart through the iliofemoral artery thus avoiding major surgery and reducing the risk to the patient. However, adequate blood flow requires that the pump and drive shaft be rotated at extremely high rpm through the bends and sharp curves of the iliofemoral and aortic arteries and therefore, extreme care must be taken to avoid creation of hot spots in the arteries.
Another disadvantage associated with high rpm blood pumps is the high risk of damaging a substantial percentage of the blood cells of the blood. Damaged blood cells are expelled by the body and new blood cells must be generated to replace them. This may create additional strain on the system of a patient who is already in critical condition. The prior art has thus been unable to provide an easily implanted low risk temporary circulatory assist pump capable of providing sufficient blood flow to assist a heart so that the heart may heal itself or keep the patient alive while waiting for a transplant to become available.